1. Field of Art
This invention relates to sealing of containers and in particular to a method of induction heat sealing foil membranes on containers.
2. Brief Description of the Prior Art
The prior art is replete with disclosures of various systems for induction heat sealing metal foil membranes on containers of various materials of construction. For example, U.S. Pat. No. 3,892,351 to Johnson et al discloses apparatus for rotating container assemblies as they are moved parallel to an induction heating coil to induction heat seal a metal foil membrane on a composite container. The composite container has a metal foil lining which is rolled outwardly into a bead at the end to which the metal foil membrane is sealed. U.S. Pat. No. 4,017,704 to Collins et al discloses another technique for induction heat sealing containers using an induction heating coil having a metal core in the center thereof for adjusting the maximum flux density of the magnetic field produced by the coil. U.S. Pat. Nos. 3,694,609; 3,748,422; 3,808,074 and 3,909,326 provide additional disclosures of methods and apparatus for induction heat sealing metal foil membranes on containers.
Despite the many prior art systems for induction heat sealing foil membranes on containers, none of the systems have gained commercial acceptance. The systems have been either unreliable, too slow or too expensive, especially for induction heat sealing composite containers. Spirally wound composite containers typically have a lap seam which results in a hump and/or crevice in the rolled edge of the container to which the foil membrane is sealed. The curved surface of the rolled edge also provides a poor sealing surface because it is relatively narrow and may have irregularities in it.
An induction heat sealing system is desired for reliable, high speed, production sealing of metal foil closures on containers.